fix(themes): re-measure nodes on level change and theme swap

The new Whimsy theme (6682cb2) exposed a latent node-sizing bug.
NodeItem measured itself on ItemSceneHasChanged, but
MindMapScene::addNode (and AddNodeCommand::redo) set the parent
*after* addItem — so level() was 0 at measurement time and every
node briefly got sized with rootStyle. With themes whose rootStyle
barely differs from nodeStyle (default, tinted, ...) the effect was
invisible, but Whimsy's Georgia 22pt rootStyle made every child take
on root dimensions, producing oversized rectangles.

  - setParentNode now re-measures on level change, so the existing
    addItem-then-addChild order produces correct sizes.
  - setThemeId re-measures every node (new public refreshGeometry)
    and refreshes edges, so a theme swap picks up padding/font/min-max
    width changes instead of keeping the previous theme's dimensions.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: broccoli-97

src/scene/MindMapScene.cpp

@@ -180,11 +180,17 @@ void MindMapScene::setThemeId(const QString& id) {
     m_themeId = id;
     // Force every node to drop its device-coord cache so a theme swap repaints
     // with the new fill/border/edge style instead of the stale cached pixmap.
+    // Also re-measure each node — themes differ in padding/font/min-width, and
+    // without a refresh the m_rect stays at the previous theme's dimensions.
     const auto items = this->items();
     for (auto* it : items) {
         it->setCacheMode(QGraphicsItem::NoCache);
+        if (auto* node = dynamic_cast<NodeItem*>(it))
+            node->refreshGeometry();
         it->update();
     }
+    for (auto* e : m_edges)
+        e->updatePath();
     for (auto* v : views())
         v->viewport()->update();
 }

src/scene/NodeItem.cpp

@@ -508,7 +508,13 @@ NodeItem* NodeItem::parentNode() const {
 }
 
 void NodeItem::setParentNode(NodeItem* parent) {
+    if (m_parentNode == parent)
+        return;
     m_parentNode = parent;
+    // Level changed → re-measure. Themes whose rootStyle overrides padding or
+    // font (e.g. Whimsy: Georgia 22pt) would otherwise leave a child sized
+    // for level=0 when it was added to the scene before being parented.
+    updateGeometry();
 }
 
 QList<NodeItem*> NodeItem::childNodes() const {
@@ -600,6 +606,10 @@ QRectF NodeItem::nodeRect() const {
     return m_rect;
 }
 
+void NodeItem::refreshGeometry() {
+    updateGeometry();
+}
+
 void NodeItem::moveSubtree(const QPointF& delta) {
     moveBy(delta.x(), delta.y());
     for (auto* child : m_children) {

src/scene/NodeItem.h

@@ -47,6 +47,10 @@ class NodeItem : public QGraphicsObject {
     QRectF nodeRect() const;
     void moveSubtree(const QPointF& delta);
 
+    // Re-measure this node against the current theme/template. Call after a
+    // theme swap so existing nodes pick up new padding/font/min-max widths.
+    void refreshGeometry();
+
     void showAddButton();
     void hideAddButton();